On Tue, 23 Mar 2010, Benedikt Huber wrote:
* Type witnesses
Type witnesses are really neat when writing darcs library code and helped to
prevent some mistakes there (escaping of type variables). But they are also
inconvenient to build at the moment and not easy to understand at the
beginning.
The sudden flurry of people using darcslib and the usage scenarios they've
got have convinced me that we really need to sort this out.
Right now I'm trying to fill in the gaps so that we can build actual
running code with witnesses on. If and when that's done, we'll have to
decide what the default should be and whether we should make them
unconditional and drop the CPP. We're also crying out for proper
documentation of them.
At the GUI / external tool level, we did not need them so far, because
of working with sealed primitive patches and PatchChoice only. The
Sealed2 type was fine, but added some clutter, requiring 'unseal2' at
many places. Maybe using darcs library at a level so low it requires
type witnesses will easily lead to corrupted repositories anyway.
I think that the type witnesses will be quite a big help in protecting
clients from corrupting things. I do realise they're a pain though.
Cheers,
Ganesh
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